As used herein "electrolytic cell" means an assembly which at least includes an anode in an anode compartment and a cathode in a cathode compartment, wherein the anode compartment and the cathode compartment are separated by an ion exchange active membrane.
"Electrolytic unit" means an assembly which at least includes two electrode components separated by a central support element. The electrode components in an electrolytic unit may be oppositely charged, as is the case in a bipolar unit, or similarly charged, as is the case of a monopolar unit. Thus, monopolar units could be either cathode units or anode units.
"Electrode component" means an electrode or an element associated with an electrode such as a current distributor grid or current collector. The component may be in the form of a wire mesh, woven wire, punched plate, metal sponge, expanded metal, perforated or unperforated metal sheet, flat or corrugated lattice work, spaced metal strips or rods, or other forms known to those skilled in the art.
Chlorine and caustic are large volume, basic chemicals which are most frequently produced electrolytically from an aqueous solution of an alkali metal chloride in electrolytic cells. Recently, a variety of technological advances have occurred to minimize the gap between the anode and the cathode of an electrolytic cell to minimize the electrical resistance of the electrolytic cell, thus allowing the electrolytic cell to operate more efficiently. Advances include such things as dimensionally stable anodes, ion exchange membranes, depolarized electrodes, zero gap cell configurations, and solid polymer electrolyte membranes.
There are two major types of electrolytic cells commonly used for the production of chlorine and caustic, i.e., monopolar cells and bipolar cells.
A bipolar electrolytic cell consists of several electrochemical units in a series, in which each unit, except the two end units, acts as an anode on one side and a cathode on the opposing side. Electrolytic units are sealably separated by an ion exchange active membrane, thereby forming an electrolytic cell, or series of electrolytic cells. Electrical energy is introduced into a terminal bipolar cell at one end of a series of bipolar cells, passes through the series of bipolar cells, and is removed from the terminal cell at the other end of the series. An alkali metal halide solution is fed into the anode compartment(s) where a halogen gas is generated at the anode. Alkali metal ions are selectively transported through the ion exchange active membrane(s) into the cathode compartment(s) where alkali metal hydroxides are formed.
Monopolar electrolytic cells comprise at least two terminal cells and a plurality of anode units and cathode units alternately positioned therebetween. The monopolar electrolytic units are separated by an ion exchange active membrane, thus forming a plurality of monopolar electrolytic cells. Each electrolytic unit is equipped with at least one inlet, through which electrolyte may be fed to the unit, and with at least one outlet, through which liquids and gases may be removed from the unit. Each electrolytic unit is electrically connected to a power supply. Power if fed to one monopolar electrolytic unit and is removed from at least one adjacent electrolytic unit.
To take advantage of the new technological advances, a variety of electrolytic unit designs have been proposed. However, many of these are quite complicated and require the use of expensive materials. An uncomplicated electrolytic unit employing readily available, inexpensive materials would be highly desirable. It is the object of this invention to provide such an electrolytic unit.